1. Field of the Invention
The invention relates to an image forming apparatus, and an image forming method, for forming images using electrophotography.
2. Description of the Related Art
An image forming apparatus using electrophotography (hereinafter often simply referred to as image forming apparatus) is at present widely used in various fields due to its capability of printing a high quality image on a recording medium with a simple operation. The image forming apparatus includes a photoreceptor drum, a charging section, an exposing section, a developing section, a transferring section, and a fixing section. The photoreceptor drum has a photosensitive layer on its surface. The charging section charges the photoreceptor drum surface to predetermined polarity and potential. The exposing section forms an electrostatic latent image on the photoreceptor drum surface that is in the charged state. The developing section supplies a toner to the electrostatic latent image on the photoreceptor drum surface to form a toner image. The transferring section transfers the toner image formed on the photoreceptor drum surface onto a recording medium. The fixing section fixes the toner image onto the recording medium. An image corresponding to image information is formed on the recording medium by the above-described processings by the sections.
In the image forming apparatus, control of toner density in the toner image, which is called process control, is executed in order to obtained a high quality image.
The process control includes a high density correction processing for setting of black solid image density, an halftone correction processing for setting of halftone level density, and a registration correction processing for setting of transfer position displacement.
In the process control, a plurality of toner patches (toner images) wherein toner densities are continuously varied by, for example, continuously changing a development bias voltage are firstly formed on the photoreceptor drum surface. The toner densities of the toner patches are detected by a toner density detection section, and the detection result is inputted to a control unit provided in the image forming apparatus. The control unit compares the detection result and a reference toner density that has previously been inputted to judge the toner patch having the toner density that is closest to the reference toner density, and specifies a development bias voltage value to be used for forming the toner patch. By forming a toner image on the photoreceptor drum surface based on the specified development bias voltage value, toner images having densities similar to the reference toner density are stably formed. In the process control, it is possible to adjust the toner densities by changing a charging voltage, an exposure potential, and the like of the photoreceptor drum without limitation to the development bias voltage.
As described above, the process control is a very important control for stabilizing toner densities, i.e. image quality of outputted image.
It is in general possible to obtain high image quality outputs by performing image quality adjustment at a frequent cycle due to prevention of deviation from the reference toner image, but the adjustment consumes time. Further, since deterioration of a developer is promoted by the patch creation due to the above-described patch creation for the adjustment, frequent adjustment is not preferable.
An image forming apparatus disclosed in Japanese Unexamined Patent Publication JP-A 2005-249873 has a judgment section judging, when power is turned on, whether or not image stabilizing processing is required for each of color modes.
As described in the foregoing, since a considerable time is required when the image quality adjustment is frequently executed, a situation of not capable of printing occur when printing is needed to incur inconvenience to a user wanting to output urgently.
An image forming apparatus disclosed in JP-A 2005-249873 simply judges whether or not the image stabilizing processing (image quality adjustment) is required, and many processings are executed in the end in a case where it is judged that the image stabilizing processing is required. Also, image stabilizing processing other than that executed when turning on the power is not considered at all.